The present invention relates to an open-end spinning apparatus with a spinning rotor into which opens a yarn takeoff channel and a fiber feed channel, and the internal space of which is connected to a source of reduced pressure.
The reduced pressure in the spinning rotor required for spinning is produced in most open-end spinning machines by means of their own source of reduced pressure, since the bores in the spinning rotor (DE-OS 2,651,551) for self-generation of reduced pressure lead to production of much noise and are easily dirtied, and the reduced pressure is always dependent on the rotational speed of the spinning rotor. When using external suction, independently of the rotational speed of the rotor, constant reduced pressure conditions are always present in the spinning rotor.
With separate sources of reduced pressure, the air is as a rule sucked away over the edge of the spinning rotor, through the gap between the spinning rotor and the rotor cover. The air thus undergoes strong friction and is strongly throttled; and as a result, dust entrained with the air is deposited on the rotor edge. These deposits break off from time to time and reach the collecting surface of the spinning rotor where they are again deposited and cause irregularities such as, for example, thick places, moire effects, or even breaks in the yarn.
It is also already known to introduce suction through the rotor cover so that no dust deposition on the rotor edge occurs (DE-OS 1,710,015, FIG. 1). Since yarn takeoff occurs here through the hollow rotor shaft and thus axially opposite the suction opening in the cover, the yarn when fed back into the spinning rotor during piecing-up is seized by the suction air stream in the cover, so that piecing-up with the reduced pressure operating for spinning is not possible. It is thus necessary to first feed into the spinning rotor the amount of fiber required for piecing-up, then to switch off the action of the source of reduced pressure, and to restart the action of the source of reduced pressure only after successfully piecing-up. This requires a very accurately timed and costly control of fiber feed, reduced pressure source or associated valves, thread backfeed, and yarn takeoff, so that there is a danger of a yarn break occurring before the reduced pressure and the fiber feed which operate in dependence on it are switched on again.